This invention relates to a portable telephone set for use in a mobile communication system and, in particular, to a portable telephone set operated in the mobile communication system comprising a plurality of base stations each of which transmits an area identification signal indicative of an area identifier assigned to a radio zone in which the base station in question is disposed.
As one of such mobile communication systems is known a mobile cellular telephone system of the EIA/TIA (Electronic Industries Association/Telecommunications Industry Association) standard. The mobile cellular telephone system comprises a plurality of base stations and a plurality of portable telephone sets or mobile stations. The base stations are disposed in respective radio zones. Each base station is connected to an exchange station. Each of the portable telephone sets is located in one of the radio zones at a time.
The radio zones are assigned with area identifiers for identifying the radio zones. In the mobile cellular telephone system, each base station transmits on a downward control channel at a constant time interval, as binary data, an area identification signal indicative of the area identifier identifying the radio zone for the base station in question in accordance with a format defined by the EIA/TIA standard [EIA/TIA-553 issued by Electronic Industries Association]. Each portable telephone set receives a plurality of area identification signals transmitted on the downward control channel to determine, as a current area identification signal therefor, one of the area identification signals that has the strongest electric field thereamong. In addition, each portable telephone set determines whether or not the portable telephone set is located in or out a home system on the basis of the current area identification signal and carries out control of operation of location registration on the current area identification signal.
Assignment of the area identification signals are different in respective countries of the world from one another. For instance, different area identification signals are assigned to respective cities and respective operator companies in the United States of America while a plurality of area identification signals are assigned to each operator company in the United Kingdom. In addition, inasmuch as methods of the assignment are entrusted to the respective operator companies, different methods of assignment are used in the respective countries of the world from one another.
In the above-mentioned mobile cellular telephone system, each portable telephone set returns, in response to an incoming call signal or a paging signal, a page response signal for the portable telephone set to the base station on which the portable telephone set belongs. It is assumed that an answering signal is not sent to the base station because an off-hook operation is not carried out by a user for the portable telephone set. In this event, in general, the exchange station connected to the base station only sends, on a channel, a ring back tone indicative of during of incoming call to a caller. If the exchange station has an incoming transfer function, the exchange station calls a telephone terminal having another telephone number which is preliminarily registered therein when the answering signal is not sent from the portable telephone set within a predetermined time interval.
It is assumed that the portable telephone set has an automatic answering function. In this event, when the predetermined time interval elapses since the incoming call signal is received, the portable telephone set carries out an automatic answering operation to record a message of the caller if the automatic answering function is turned on or activated. In addition, there is another mobile cellular telephone system which comprises the exchange station having the automatic answering function.
It is presumed that a user of the portable telephone set cannot carry out response operation (answering operation) because the user is present in another place due to a meeting, a job or the like with the portable telephone set left although the user receiving the incoming call is within an area enabling telephone conversation. In this event, in prior art, the ring back tone is sent from the exchange station to the caller or the telephone terminal having the other telephone number is called by the incoming transfer function of the exchange station. Accordingly, the caller cannot confirm a location of the portable telephone set for an opposite party.
In addition, although the message of the caller is recorded by using the automatic answering function, the caller cannot confirm the location of the portable telephone set for the opposite party until the opposite party establishes connection with the caller.
In order to solve such a problem, various systems are already known. By way of example, a paging system is disclosed in Japanese Unexamined Patent Prepublication of Kokai No. Hei 4-294,644 (294,644/1992) for Japanese Patent Application No. 83,446 of 1991. The paging system attains effective utilization of a receiver by displaying a map representing a current location of a possessor of the receiver and a location of an opposite party onto a display section. The paging system according to Kokai No. Hei 4-294,644 comprises a plurality of subscriber telephone sets installed in fixed locations, a base station including a storage section for storing location information indicative of the fixed location of each of the subscriber telephone sets, and a paging receiver with display for displaying map information indicative of a map.
In the paging system, the base station is provided with the storage section for storing the location information indicative of the location of each of subscriber telephone sets. The paging receiver with display is formed to display the map information. A prescribed format signal is sent to the base station through the subscriber telephone sets. On receiving the format signal, the base station sends a signal including the location information indicative of the location of the subscriber telephone set. On reception of the signal including the location information, the paging receiver displays the map information indicative of the map representing the location of the subscriber telephone set. Moreover, on reception of the format signal, the base station calculates a route between the subscriber telephone sets and sends a signal including the location information indicative of the location and route information indicative of the route. On reception of the signal including the location information and the route information, the paging receiver displays map information indicative of another map representing the location of the subscriber telephone set and the route between the subscriber telephone sets.
However, the paging system according to Kokai No. Hei 4-294,644 has a lot of hardware and much software because the base station must be provided with the storage section for storing the location information indicative of the location of each of the subscriber telephone sets.
Japanese Unexamined Patent Prepublication of Kokai No. Hei 5-276,067 (276,067/1993) for Japanese Patent Application No. 68,688 of 1992 discloses a radio communication equipment which sends position information to a communication opposite party automatically by using a GPS reception section so as to receive a signal from a GPS satellite and to calculate position information data and sending the data together with voice information. The radio communication equipment according to Kokai No. Hei 5-276,067 comprises a transmitter section and a receiver section. The transmitter section comprises the GPS reception section, a microphone, and a transmission section. The receiver section comprises a reception section, a position data voice separation section, a speaker, a position information decoding section, and a position information display section.
On receiving a signal from the GPS satellite, the GPS reception section calculates position information data. The transmission section sends the position information and a voice signal via a microphone to a communication opposite party continuously. On receiving a signal from the transmitter section by the reception section of the communication opposite party, the position data voice separation section separates the signal into the position information data and the voice signal. The position information data is displayed on the position information display section while the voice signal is reproduced by the speaker. Thus, the radio communication able to send the position information to the communication opposite party is automatically realized without oral contact.
However, the radio communication equipment according to Kokai No. Hei 5-276,067 is expensive because the radio communication equipment comprises not only a transmission/reception section for intercommunication but also the GPS reception section for receiving the signal from the GPS satellite.
Japanese Unexamined Patent Prepublication of Kokai No. Hei 5-328,432 (328,432/1993) for Japanese Patent Application No. 152,768 of 1992 discloses a cordless telephone system which easily confirms a location of a cordless telephone set of an opposite party when an extension call is implemented between cordless telephone sets. The cordless telephone system comprises a master set, a plurality of cordless telephone set connectors, and a plurality of cordless telephone sets. The cordless telephone set connectors form radio zones. The master set comprises a call processing section including an extension processing section, a memory section including a position registration information storage section, an external line interface section, a channel switch section, and a cordless telephone set connector interface section connected to the cordless telephone set connectors.
The cordless telephone sets use a cordless telephone set connector whose radio wave reception state is best among the cordless telephone set connectors. In the case of extension call among the cordless telephone sets, the extension processing section refers to the position registration information storage section in which the information of a radio zone relating to the cordless telephone set connector used by each of the cordless telephone sets to acquire the radio zone corresponding to the cordless telephone set connector by the caller and the called telephone sets and sends the acquired caller and called radio zones to the called and the caller cordless telephone sets as data to be displayed a display device of the called and the caller cordless telephone sets.
However, the cordless telephone system according to Kokai No. Hei 5-328,432 has a lot of hardware and much software because the master set must be provided with the position registration information storage section for storing the information of the radio zones relating to the cordless telephone set connectors used by the cordless telephone sets.